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Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4487
Experience:  15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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I have a S550 2007 and there is an on and off noise (not

Customer Question

Hi. I have a S550 2007 and there is an on and off noise (not load) comming from the engine compartment when I'm driving, a kind of groan og like something is struggling, and sometimes is continues after I have stopped and turned the engine off - any ideas?
JA: How many miles are on the car? Is it an automatic or a manual transmission?
Customer: Hi again. Have you any ideas for me on the problem? Regards. Jon Gardar
JA: Are you fixing your S550 yourself? What have you tried so far?
Customer: No I am not fixing it myself, I went to a repair shop the other day but then we couldn't here it (it's not always). So now I'am just wondering if this could be a sign that something's dry, possibly a suspension component, and it could be fixed by lubrication? Have you heard of something similar you could tip me with?
JA: Anything else you want the mechanic to know before I connect you?
Customer: No I think thats it - thanks.
Submitted: 11 months ago.
Category: Mercedes
Expert:  Lou P. master tech replied 11 months ago.

Hello, my name is***** and i will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

Expert:  Lou P. master tech replied 11 months ago.

Not sure why my last reply did not come through, i have been having site issues, so sorry!

get me your vin i think that is the air compressor noise for the air suspension that you are hearing i want to confirm you have airmatic and not abc. again so sorry that my last response did not come through :(

Customer: replied 11 months ago.
Hi again Lou and many thanks for your reply - and no worries about your last response :)
I think my car has airmatic, but how would I know if I wanted to check?
And if its the air compressor noise for the air suspension, how will I fix that?
Looking forward to hearing from you again, thanks!
Expert:  Lou P. master tech replied 11 months ago.

Jon thanks for the patience man, so sorry again, so the quickest way to know is to open the hood and at the top of the shock tower you will have an air line in it , if not it will be an electrical connection.

for the compressor check

and i can get you instructions if needed. let me know!

Expert:  Lou P. master tech replied 11 months ago.

or just get me your vin and i can check the build sheet. :)

Customer: replied 11 months ago.
Sorry mate, but whats a "vin" ?
Expert:  Lou P. master tech replied 11 months ago.

Vehicle Identification Number

the 17 digit number that you use to register a car and insurance and all that jazz, its on the windshield frame in a small window and also on the door sticker on drivers side front door.

Customer: replied 11 months ago.
Got it, hope its ok I sent it tomorrow?
Expert:  Lou P. master tech replied 11 months ago.

yes Jon no worries send it when you have the time, we are not timed and i am in no hurry on my end, my only hurry is to get you fixed up quick

Customer: replied 11 months ago.
Thanks again Lou, appreciate it - here is the vin : WDDNG86X18A170125
Expert:  Lou P. master tech replied 11 months ago.

yes you have airmatic.

the air suspension. so the compressor is under the passenger front of the bumper. when starting the car you should hear a nice hum from it, if it sounds like marbles in a tin can it is bad. it can still be bad with a nice hum but at least we will know the circuitry will be good .

ill send over instructions on how to replace it, BUT dont go replacing it just yet, confirm that is does or does not turn on.

Expert:  Lou P. master tech replied 11 months ago.

sorry i was on auto pilot for a failing air compressor lol, so yes the noise you are hearing will be from the air compressor kicking on and off, if you are noticing it more and more then the compressor is most likely failed , rarely the mounts can come loose so the compressor vibrates in the bracket but for the most part its the compressor that you are hearing as long as you can confirm that it is coming from the passenger front of the car,

Expert:  Lou P. master tech replied 11 months ago.

you can get the compressor from

your oem part number is




those are the numbers, the compressor was updated a few times, so the first is the oldest and the last is the newest, any compressor that you find that relate to those numbers will work. also purchase a relay as well. .

part number


the relay fails after years of use and will stick closed and cause the compressor to run on until it burns up and the fuse blows. so we always change those at the same time as any work is done on the system, hope this info helps, please let me know if you have any more questions or need any more info

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